It is generally desirable to make radio frequency technology more compact so that the devices carrying the technology can be made smaller or so that the technology can be integrated into devices that at present do not include the technology.
One problem associated with radio frequency technology is that at least one antenna element is required to be able to transmit radio frequency signals and/or to receive radio frequency signals. It is a difficult problem to design a radio frequency antenna element that has an acceptable efficiency in a frequency band of interest and which is also of a small size.
Performance of an antenna element is dependent upon the size of the antenna element as there is generally a relationship between the physical size of the antenna element and it's electrical length and also a relationship between the electrical length of the antenna element and it's resonant modes.
Furthermore, the size of a separation of an antenna element from other conducting components such as a ground plane or Printed Wiring Board can dramatically affect the performance of an antenna element. An antenna element may therefore need to be separated from a Printed Wiring Board by some distance to achieve acceptable performance. This places a constraint on the minimum size of a device that can house the antenna element and Printed Wiring Board.
Some antenna elements are required to operate in more than one band. For example, a cellular communication device may need to operate in one band at one time and a different band at a different time. It is a difficult problem to design a multi-band radio frequency antenna element that has an acceptable efficiency in a frequency band of interest and is also of a small size.
Definitions
A ‘microwave circuit component’ is defined as a class of components that includes lumped reactive components (e.g. capacitors and inductors) and distributed reactive components (e.g. transmission lines) but excludes antennas. Microwave circuit components do not produce effective far-field radiation.